“Masks prevent you from giving it to someone else not you from everyone else.”
Why would a properly fitted and clean N95 combined with eye protection and gloves, and properly handled at removal, not protect you? The manufacturers (e.g. 3M) certainly do claim they will.
That’s not what they are talking about doing, yes all that gear would protect you to a large extent.
Where it fails is, is the person falsely thinks they are perfectly protected and doesn’t engage in hand washing and transfers the infection to themselves from a surface (could be the gear they were wearing) on to themselves or puts themselves more at risk and gets exposed through close contact with someone not similarly protected (person removing their mask to sneeze).